Method of precoating a filter cartridge

ABSTRACT

An improved precoat filter cartridge and a method of applying the precoat medium thereto. The filter cartridge comprises: a vertically extending tubular core element having apertures therein; a filter screen positioned about said core element to receive precoat particles; and a cover member closing off the upper portion of said core element defining a chamber formed by the sides thereof to accumulate gas trapped within said cartridge. A vent hole is provided in said cover member to permit the trapped gas to be vented therethrough.

United States Patent [151 3,680,700 [451 Aug. 1,1972

Ryan

[54] METHOD OF PRECOATING A FILTER CARTRIDGE [72] Inventor: Leo F. Ryan, Somerville, NJ. [73] Assignee: Ecodyne Corporation 221 Filed: Nov. 9, 1970 [21] Appl. No.: 87,661

[52] U.S. Cl ..2l0/7S [51] Int. Cl. ..B01d 37/02 [58] Field of Search ..210/75, 193

[56] References UNITED STATES PATENTS 3,250,703 5/1966 Levendusky ..210/75 X 3,178,021 4/1965 Bray ..210/75 X Primary Examiner-Sarnih N. Zaharna Attorney-Charles M. Kaplan and Joel E. Siege] 57 ABSTRACT An improved precoat filter cartridge and a method of applying the precoat medium thereto. The filter cartridge comprises: a vertically extending tubular core element having apertures therein; a filter screen positioned about said core element to receive precoat particles; and a cover member closing off the upper portion of said core element defining a chamber formed by the sides thereof to accumulate gas trapped within said cartridge. A vent hole is provided in said cover member to permit the trapped gas to be vented therethrough.

s Claiim, 2 Drawing Figures BACKGROUND OF THE INVENTION The present invention relates to an improved filtration system and more particularly to an improved precoat filter cartridge and method of applying the precoat medium thereto.

Liquids may be very effectively purified by passing the them through a. filter screen which has been precoated with a layer of ion exchange resin particles in the size range of 60 to 400 mesh, hereinafter referred to a precoat medium. This method is disclosed in US. Pat. No. 3,250,703, issued May 10, 1966, and assigned to the assignee of this invention.

In the typical system of this type a plurality of filter cartridges are spaced within a filter tank. Precoat filter cartridges of this type generally include a core element of suitable corrosion resistant material having openings therethrough. The body portion is covered with a layer of coarse screen which, in turn, is wrapped with a layer of .fine mesh screen. In order to precoat the filter cartridges a water slurry of precoat medium is passed through the filter tank. A precoat layer of precoat medium is thereby deposited upon the upstream sides ,of the filter cartridges. A precoat layer of uniform distribution throughout the entire length of the filter cartridges is desirable for maximum uitlization of the system.

It has been discovered that during filling of the filter tank with water a certain amount of air or other gases are trapped in the upper portion of each filter cartridge due to capillary resistance. This has at least two deleterious effects on the filtration system. Firstly, the gas prevents the flowof slurry through those areas of the cartridges in which it is located and thereby prevents precoating; and secondly during the filtering cycle of the system, gas is periodically released outwardly through the filter cartridges and disrupts the precoat thereon.

This problem of accumulated gas within the precoat cartridges is especially prevalent with precoat media having low pressure drop characteristics such as powdered ion exchange resins. The only attempts to solve this problem in the past have been attempts to minimize the gas in the incoming water entering .the system. This has not been satisfactory because of the obvious difficulty of preventing gas from entering the system.

The apparatus for carrying out the invention comprises a precoat filter cartridge having a dome shaped cover around the upper portion of the cartridge. The cover includes a vent hole communicating with the internal portion of the .filter cartridge. The invention further provides a method of precoating the cartridges which comprises: a) filling the filter tank with water at a relatively low pressure; b) increasing the pressure of the water within the tank; and c) cycling a precoat slurry through the tank. By increasing the pressure of the water within the tank prior to precoating the accumulated gas is compressed and vented through the hole in the dome shaped cover.

DESCRIPTION OF THE DRAWING Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawing, which illustrates a preferred embodiment, and wherein:

FIG. 1 is a schematic representation of a filtering system of the type which utilized the filter cartridges of the present invention; and

FIG. 2 is an enlarged partial cross sectional view of oneof the filter cartridges illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is illustrated schematically a filter system, indicated generally by the reference, numeral 10, for removing dissolved and undissolved impurities from water in accordance with present invention. Although the present invention will be discussed in detail with respect to the purification of water, the present invention has application to the purification of gasses and other liquids.

The filtration system l0 comprises a filter tank 12 having an inlet conduit 14 and an outlet conduit 16. Filter tank 12 is generally cylindrical vessel made of steel, 'or the like having outwardly convex top and bottom portions 18 and 20, respectively. Tank 12 is partitioned into aninfluent zone 22 and an effluent zone 24 by a downwardly convex tube sheet plate 26 suitably secured to the interior of the tank by welding or the like.

Inlet conduit 14 enters tank 12 through the bottom end 20 and passes upwardly through effluent zone 24 and plate 26 to communicate with influent zone 22. Conduit 14 is attached to plate 26 by welding or the like, so as to preclude fluid leakage from influent zone 22 to effluentizone 24. Fluid entering influent zone 24 through inlet conduit 14 is distributed radially outwardly'by distribution plate 28.

Mounted within the influent zone 22 are a plurality of filter cartridges 30 through which the influent stream must pass before entering effiuent zone 24 and being discharged from filter tank 12 through outlet conduit 16. Each filterv cartridge 30 is held in place in influent zone 22 of filter tank 12 by a holding assembly, indicated generally by reference numeral 32. The selection of a suitable holding assembly would, of course, be within the ordinary skill of one in the art. Holding assembly 32 is adopted .to releasa'bly hold filter cartridges 30 in place upon filter seat means 34 which are attached to plate 26. Filter cartridges 30are placed into and removed from filter tank 12 through a manhole opening 36in filter tank 12. Manhole opening 36 has a cover means 38 which may be removed or opened, as desired, to provide access to the interior of filter tank 12.

Filter seat means 34 comprises a small pipe made of steel or the like which extends through a hole in plate 26-and is attached to plate 26 by welding or other suitable means. Filter seat means 34 is substantially parallel to the longitudinal axis of filter tank 12 and connects influent zone 22 with eflluent zone 24. Filter seat means 34 provides a base for the filter cartridge 30, which is held in position on means 34.

The filter tank is also provided with a vent 39. Vent 39 may be of any suitable construction, the selection of appropriate vent means being dependent generally upon the specific use of the filter system 10.

A water slurry of the particular precoat medium (e.g. finely divided ion exchange resin particles in the size range of about 60 to 400 mesh) is stored in a precoat tank 40. A slurry line 41, controlled by a slurry valve 42, connects precoat tank 40 with a slurry pump 43. A transfer line 44 connects pump 43 with inlet conduit 14 of filter tank 12. A transfer valve 45 adjacent the pump 43 and in transfer line 44 controls the passage of slurry from pump 43. g a

I The water to be treated enters filter system through feed line 46 having an intake control valve 47. Feed line 46 is connected to transfer line 44 between controltransfer valve 45 and inletconduit 145" 1 Outlet line 16 is connected to a service line 48 and a precoat return line 49 at a T-juncture indicated by reference numeral 50. Service line 48-is connected to service units not shown, such as a steam generator and the like, and has a service valve; 51'. The precoat return line 49 is connected to the precoat tank 40 and has a return valve 52 to control the flow of flurry back to precoat tank 40. Backwash line 57 is connected to outlet line 16 and has a valve 58 to control the flow of backwash water into tank 22. A bridge line 53 with a bridge valve 54 interconnects the precoat return line 49 and the slurry line 41. Filter system 10 is equipped with a ventvalve 55 and drain valve 56. Referring to FIG. 2, each filter cartridge includes as inner core element 60 of suitable corrosion-resistant material such asv aluminum or stainless steel having holes 62 therein. Core element 60 is covered with a layer of coarse drain mesh 65 which, in turn is wrapped with a layer of fine mesh screen 68. .Filter'cartridge 30 includes a dome shaped cover member 70 closing ofi' the upper'portion'of core element 60 so as to define a chamber 71 between the side walls thereof. Vent hole 72 passes through the upper portion of cover member 70 so as to permit fluid communication between chamber 71 and influent zone 22. Core element 60 and screens'65 and 68 extend upwardbeyond vent hole 72 so as to prevent precoat material from entering chamber 71 through vent hole 72. i

V In preparing the filter system 10 for operation the initial step isto precoat the filter cartridges 30. To these ends, the filter tank 12 is filled with a low impurity water, such as demineralized water, at a relatively low pressure, i.e. approximately 8 p.s.i.. Tank 12 is filled by passing the demineralized water through backwash line 57 and into tank 12 via outlet line 16. During this filling step all the valves are closed, except valve 58 and vent valve 55. Due to capillary resistance air or other gasses may be trapped in the upper portions of cartridges 30 and in chambers 71. The pressure of the water in tank 12 is caused by the back pressure resulting from controlling valve 55. Upon filling tank 12 with demineraliz'ed waterat a relatively low pressure all valves are closed.

A slurry of precoat medium and demineralized water is prepared in precoat tank 40. The precoating step is initiated 'by' opening slurry valve 42, transfer valve 45 and returnvalve 52 and starting pump 43, thereby drawing -the precoat slurry from precoat tank .40 through transfer line 44 into filter tank 12 via inlet conduit 14. The pressure of the incoming slurry forces the demineralized water in filter tank 12 through screens 68 and 65 and core elements 60 into filter cartridges 30 and out of r the filter tank 12 via conduit 16. This demineralized water; enters the precoat tank 40 through the return line-- 49. Return valve 52 is controlled so'as tocreate a back pressure in tank 12 which increases the pressuresof the water in tank 12. By increasing the. presureof' the water'in tank 12 the gas trapped in the upper portions of cartridges 30 are compressed upward into chamber .71 and partiallyforced out through vent hole 72. Tests have shown that by doubling the pressure in tank 12 from approximately 8 to 16 psi. all the trapped gas in the filter cartridges 30 is forced upward into chamber 71 thereby permitting a uniform precoat over the entire length of the cartridges below cover member 70. This increased pressure is retained in the system during the precoat cycle and the service cycle so as to continue to confine the gas. I

As the cycling continues the precoat slurry is brought into contact with the upstream surfaces of the filter screens 68 of filter cartridges 30. The particles of the precoat medium are separated from the slurry and deposited as 'a precoat layer upon the upstream surfaces of the screens 68. The slurry is circulated through the filter system in this manner until sufiicient depth of the precoat is deposited upon the upstream surface of filter screens 68. The precoating step is terminated by closing slurry valve 42 and return valve 52 and opening bridge valve 54. Pump 43 is kept running until the recycle stream is clear. The filter system is now ready to be used to treat the service water.

The service cycle is begun by closing bridge valve 54 and transfer valve 45 and opening service valve 51 and feed valve 47. This step is preferably timed to maintain suflicient pressure in the system to assure retention of the precoat layer on filter screens 68. In this manner, untreated water enters the filter system through feed line 46, passes through transfer line 44 and passes through inlet conduit 14 to influent zone 22. The pressure of the incoming untreated water forces it through the precoat layers, filter screens 68 and and core elements 60 into filter cartridges 30 andout through outlet conduit 16. As the untreated water passes through the precoat layers, impurities are removed from the water. The treated water flows through outlet conduit 16 to service line 48.

Eventually the precoat material will become exhausted and must be replaced. At this time the filtering step is stopped by closing intake valve 47 and service valve 51. Vent valve 55 and drain valve 56 are opened to drain filter tank 12. The filter cartridges 30 are washed by an internal washing system, not described or shown. Another charge of precoat material is then placed in the precoat tank 40 and the process of precoating and filtering described in detail hereinbefore is repeated. I

It has been shown that by increasing pressure and venting the top of a filter cartridge so as to compress and expel gas trapped therein; the present invention prevents such gas from blocking flow of a slurry that is depositing a precoat on the cartridge.

Through the apparatus of the present invention has Obviously, many modifications and variations of the present invention as hereinafter set forth will occur to those skilled in the art, and it is intended to cover in the appended claims all such modifications and variations as fall within the true spirit and scope of the invention.

What is claimed is:

l. The method of precoating a hollow filter cartridge positioned within a filter tank so as to confine any gas accumulated within the cartridge, which comprises the steps of:

a. filling the tank with a liquid at a relatively low pressure;

b. introducing liquid into the tank so as to increase the pressure of the liquid within said tank and thereby compress the gas accumulated within said filter cartridge into a chamber defined adjacent the top thereof; said chamber being in direct and free communication with the filter interior and having substantially imperforate walls to confine the gas remote from the filtering area of the filter cartridge thereby permitting the precoat to deposit on said area in a uniform layer; and

c. cycling a precoat slurry through the tank so as to deposit particles on the filter cartridge as said slurry passes through said filter cartridge.

2. The method as defined in claim 1 wherein the cycling of said precoat slurry through said tank is effective to increase the pressure of the liquid within said tank and compress said accumulated gas within said chamber.

3. The method as defined in claim 2 wherein the increased pressure of the liquid within the tank is maintained during the service cycle.

4. The method as defined in claim 1 including the step of venting the gas compressed within said chamber through an aperture in communication with said chamber.

5. The method as defined in claim 1 wherein the increased pressure of the liquid within the tank is approximately double the pressure of the liquid initially filling the tank. 

2. The method as defined in claim 1 wherein the cycling of said precoat slurry through said tank is effective to increase the pressure of the liquid within said tank and compress said accumulated gas within said chamber.
 3. The method as defined in claim 2 wherein the increased pressure of the liquid within the tank is maintained during the service cycle.
 4. The method as defined in claim 1 including the step of venting the gas compressed within said chamber through an aperture in communication with said chamber.
 5. The method as defined in claim 1 wherein the increased pressure of the liquid within The tank is approximately double the pressure of the liquid initially filling the tank. 